Closures for containers in which materials are packaged for shipment, sale and storage pending use must dependably retain the material within the container and, especially if the material includes volatile constituents, must seal the container against the escape of gases or vapors. Lids of the type that are forced down into the circular openings at the tops of cans are commonly fabricated from thin steel strip and are strong enough to frictionally engage the container at the opening with sufficient pressure to ensure against unintended lifting of the lid resulting from internal pressure or other forces applied to the inner surfaces of the lids. These metal lids are relatively expensive.
For special purposes, such as the packaging of a material and an applicator in a single package unit, space is provided for the applicator in and above an inner lid which closes the can containing the material and an outer cover is provided to enclose the applicator. In the case, for example, of a package for a semisolid car wax, the wax material is contained within a can having a large mouth at its top and this can is closed and sealed by a lid that is pressed tightly down into the mouth of the can. A wax applicator is seated within this inner lid and is, in turn, held in the container unit by a stiff outer cover which snaps over the top bead of the can but does not necessarily provide a seal closure. The physical characteristics of the semisolid wax material are such that the tipping and jarring of a can, as in shipment, may cause the body of material to flow sufficiently to bear against the lid with the possible consequence of pushing it out sufficiently to permit leakage unless the lid is strong enough and is forced into the mouth of the can with enough force to have securely locked it in position.
The necessity of the outer cover of such duplex packages offers the possibility of relaxing the demands upon the inner lid in serving its closing and sealing function. In accordance with the present invention, the inner lid is made of relatively inexpensive, thin plastic material which, while capable of closing and sealing container cans of the type above referred to, is not strong enough to engage the can at its mouth with sufficient sustained pressure to hold itself tightly in place pending intentional forced removal. Instead of depending upon its own strength for this purpose, as in the case of lids made of steel, stops are provided around the inner periphery of the outer stiff cover to bear upon the flange of the inner lid at spaced locations throughout its periphery as the cover is snapped into position upon the can.
Accordingly, the principal object of the invention is to provide a duplex package which employs an inner lid of thin plastic material to close and seal the base can and an outer cover which holds the inner lid in its sealing position. This object is realized by providing the outer cover with detent means which engage the top bead of the can to hold the cover firmly down upon the can and spaced stops within the cover which bear against the flange of the inner lid when the outer cover has been snapped down into position.
A further object is to provide means for the escape of air as the lids are forced down into the mouths of the cans in the high-speed assembly line. Another object is to provide detent means on the riser portions of the inner lids which serve to hold the lids in position in the openings of the cans pending application of the outer covers.